build failure on arm-linux-gnueabihf

compiling signal.c
signal.c: In function ‘check_stack_overflow’:
signal.c:720:27: error: ‘mcontext_t’ has no member named ‘gregs’
const greg_t sp = mctx->gregs[REG_ESP];
^
signal.c:720:35: error: ‘REG_ESP’ undeclared (first use in this function)
const greg_t sp = mctx->gregs[REG_ESP];
^
signal.c:720:35: note: each undeclared identifier is reported only once for each function it appears in